18mm ply direct on joists - take up and lay 25mm?

25 Oct 2007
Reaction score
United Kingdom
Hi, we were going to lay laminate in our kitchen but on the advice of some posters we are going for tiles.

Half the floor is currently 18mm ply direct on to the joists. Reading on here it says 18mm might have too much flex for tiles. Is it advisable to take it up and replace with 25mm ply or could we just lay 6mm or 9mm ply ontp of the old ply?


Sponsored Links
Hi John, glad you made the right choice! :D
Ok now the sleeves are up and we can get down to business. First off, you're going to get mixed opinions as to whether 18mm ply is good enough to tile on. I sit firmly in the "it's not thick enough" group because I feel that, unless very well supported, 18mm just isn't rigid enough to support tiles reliably.

Assuming you agree with this, you're going to need to do some work on your floor. There're two options I would recommend to you here:
Option 1 - You take up the current floor and replace with 25mm WBP ply, screwed down every 300mm to the joists. Don't forget to stagger the joints and make sure that you add extra support (noggins) under sheet edges between the joists. Then tile using Bal single part flexible adhesive and Bal superflex grout.
Option 2 - You ensure that the existing ply is screwed to the joists every 300mm. You then overboard with 9mm (use 12mm if your existing floor is springy) WBP ply which needs to be screwed down every 200mm all over the face of the sheets. Again, stagger the joints. Then tile using Bal single part flexible adhesive and Bal superflex grout.

Now option 2 is fine and will work no problem, but if you are prepared to replace the floor as in option 1 then that would result in a bomb proof job.
You mentioned in a previous post about needing to stick ply to tiles to bring the height up to match the rest of the floor - now you're tiling, you want to be sticking the ply down with the tile adhesive mentioned above and not gripfill.
A word on adhesives..... the adhesive I recommended is expensive but is vital - don't be tempted to save a few quid on a cheaper brand. It pays to search around for a good price - have a look online.
Good luck.
cheers gcol.

The current joists doesn't have noggins where the ply ends so I guess it i option 1 I'll go for.

If I put the noggins in will normal 3*2 stud timber suffice for these or do i need to go for noggins that roughly the same size as the joists?

Also as we're going for tiles we'll go for an electric tile warmer. Is picking one up from Wickes or the like OK or is there a recommended make?

cheers for all your advice again and saving us from doing a botch job!
Good choice.
3x2 is fine.
As for under floor heating, I suggest you go to a good tile shop and ask them what they recommend. New products are coming out all the time and as I'm no longer in the tiling game I'm a little out of touch with what's new in under floor heating.
Personally speaking though, I wouldn't bother with it - I have all the downstairs tiled in my house and don't find it a problem without heating.
Sponsored Links
if your 18mm ply is screwed down securely i would overboard with 9mm ply and screwed at 150mm centres, use a good flexi adhesive such as bal and a good flexi grout, again such as bal, too many decent UFH mats to recommend just 1.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local